a) Field of the Invention
The present invention relates to an audio amplifier and more particularly an audio amplifier which is capable of producing relatively high power output, while operating with relatively low power losses, and also being of relatively small size.
b) Background Art
An audio signal is characterized in that it comprises what might be called a series of xe2x80x9cpeaks and valleysxe2x80x9d. There are periods of high amplitude (the peaks) and also those periods of relatively low amplitude (the valleys). The total of the time periods for the xe2x80x9cpeaksxe2x80x9d is in most all instances rather small, compared to the total of the time periods for the valleys. This is true even of music which would be considered consistently loud music, such as hard rock.
This imposes somewhat unique problems in the design of audio amplifiers, and yet provides opportunities for technical improvements. Thus, it is the object of the present invention to provide an improved audio amplifier which is of a relatively small size, operates quite efficiently, is relatively inexpensive to manufacture, and yet is capable of faithful amplification of audio signals.
The audio amplifier of the present invention is able to deliver relatively high power output (2,000 watts or more) and yet be small in size and operate with relatively high efficiency.
In a first embodiment this amplifier comprises a power amplifier section which receives an audio input signal and positive and negative power inputs to produce an audio output. There is also a power supply comprising a positive power supply section and a negative power supply section.
The positive power supply section comprises a transformer having a primary and a secondary winding, with a secondary winding being connected to the power amplifier section to supply positive voltage power input to the power amplifier section.
There is a power switch for the positive power supply section to supply current pulses to the primary winding. There is also a filter circuit component connected to an output of the secondary winding of the transformer to maintain the voltage of the positive power output as a continuing variable voltage input.
There is also a control circuit responsive to an audio input signal to transmit a pulsed control signal to the switch section to cause the switch section to open and close in a manner to transmit current pulses to the primary winding of the transformer. The pulses have a proportional relationship to the strength of the audio signal, so that the positive voltage input to the amplifier section tracks the audio signal in a manner to maintain the positive input voltage at a predetermined level range above voltage of the audio input.
The negative supply section also comprises a transformer, a second power switch section, and a filter circuit component. However, the negative power supply section provides a negative voltage power input to the power amplifier at a voltage below the audio signal voltage by a predetermined amount. In other respects, the negative power supply section is constructed and operates in substantially the same manner as the positive power supply section. The negative power supply section is controlled by the control circuit.
In the first embodiment, the switch section for each of the power supply sections comprises two switches connected to opposite sides of the primary winding of the transformer. The pulses of one of these switches passes through the related primary winding in one direction, while the pulses of the other switch pass through the related primary winding in an opposite direction, in an alternating sequence. An intermediate portion of each of the primary windings in connected to a power source.
Also, the secondary winding in the first embodiment is connected to ground at an intermediate location of each secondary winding.
The control circuit comprises a pulse width modulator which receives a clock input to initiate successive pulse signals. The pulse width modulator also has an audio signal input to cause the pulse width modulator to transmit pulse signals having a pulse strength with a proportional relationship to the audio signal. The positive component of the audio signal controls the first power switch section and the negative component of the audio signal controls the negative power switch section.
In the preferred form, the pulse width modulator creates square wave signal pulses, with the width of the pulses varying in accordance to the amplitude of the audio signal.
In the first embodiment, the secondary winding of the two power supply sections has two end connections and first and second diodes to receive the output at each of the end connections with the output of the diodes being directed to the power amplifier section.
The control circuit operates to close each set of first and second switches alternately, so that the current pulses from each secondary winding are transmitted alternately through the first and second diodes.
In the preferred form of the first embodiment, each filter circuit component comprises an induction coil to receive the output of the secondary, and a capacitor connected at a location between the induction coil and the amplifier section.
In the method of the first embodiment of the present invention, an audio amplifier is provided as noted above. Each pulse width modulator transmits pulses to the first and second switch sections of each power supply section, with the width of the pulses having a proportional relationship to the amplitude of the audio signal. The pulses from each set of switches is transmitted to its related transformer, which in turn transmit these pulses through the related filter circuit component and thence to the power amplifier section.
In a second embodiment of the present invention, there is, as in the first embodiment, the power amplifier section, the power supply comprising a positive power supply section and a negative power supply section, and also the control circuit. The two power supply sections differ from the first embodiment in several ways.
In each power supply section of the second embodiment, there is an amplifier having primary and secondary windings, and each primary winding has first and second switches in series with the primary winding at first and second opposite ends, respectively, of the primary winding. The amplifier and the control circuit are arranged so that the first and second switches of each power supply section open substantially simultaneously and close substantially simultaneously to cause the pulse to be transmitted through the secondary winding. The secondary winding is connected to a first diode that in turns connects to the power amplifier section to enable pulses generated in the secondary winding to travel through the first diode to the power amplifier. These are arranged so that current flows through the primary winding and the secondary winding substantially simultaneously. Each filter component comprises a capacitor connected to the first diode and the power amplifier section, and there is an induction coil. Additionally, there is a secondary diode positioned between the induction coil and the first diode which is arranged to be nonconductive when the first diode is transmitting a pulse, and to be conductive when the first diode is turned off.
The first switch of each power supply section connects to a power source, and the second switch connects toward a ground connection. A diode is connected from a location between the first end of the transformer and the second switch, toward a ground location. Also, a diode is connected from a location between the second end of the transformer and the second switch to connect toward a power connection location.
There is a third embodiment of the present invention which is rather similar to the first embodiment, except that the transformer of each power supply section is arranged in a manner that when the first and second switches of each power supply section are closed an impulse of current flows through the primary winding of the transformer, no current is flowing in the secondary winding, and after the first and second switches are opened a collapsing field of the primary winding induces current to flow through the secondary winding.
In this third embodiment, there is a diode connected between the secondary winding of each power supply section and the power amplifier section to permit current from the secondary winding of each power supply section after the current pulse has passed through the primary winding and the current pulse is induced in the secondary winding.
The control circuit of the present invention comprises a pulse width modulator which receives a clock input to initiate successive pulse signals, and having an audio signal input to the pulse width modulator to transmit pulse signals having a pulse width with a proportional relationship to the audio signal. The control circuit comprises a first control circuit portion which receives positive portions of the audio signal and generates pulse control signals corresponding to the positive audio signal portions, and a second control circuit portion which receives negative portions of the audio signal and utilizes the negative portions of the audio signal to produce pulse control signals control pulses for the negative power supply section. Also, in the preferred form, the power supply comprises a power source which delivers DC power to each of the power supply sections. Also, in the preferred form, the DC power directed to each of the power supply sections is of the same polarity.
The method of the second and third embodiments is sufficiently similar to the method of the first embodiment so that it is believed no detailed explanation of the same is needed at this portion of the text.
Other features will become apparent from the following detailed description.